Koh Junichi, Kubota Tetsuro, Koyama Toshiko, Migita Tomofusa, Hashimoto Mitsumasa, Hosoda Yoichiro, Kitajima Masaki
Department of Surgery, Saitama Social Insurance Hospital, 4-9-3, Kitaurawa, Saitama-shi, Saitama 330-0074, Japan.
Breast Cancer. 2003;10(3):260-7. doi: 10.1007/BF02966727.
7-Hydroxystaurosporine (UCN-01) was originally isolated as a protein kinase C inhibitor and has shown antitumor activity against several human cancer cell lines. UCN-01 inhibits cell cycle progression from the G1 to the S phase and is associated with inhibition of cyclin-dependent kinase (CDK) activity and induction of intrinsic CDK inhibitor p21, leading to dephosphorylation of retinoblastoma (Rb) protein. Tamoxifen (TAM) traps cancer cells in the G1 phase, suggesting that the mechanism of action of TAM is similar to that of UCN-01. The present study was conducted to assess the antitumor activity of UCN-01 combined with TAM against human breast carcinoma cells in vitro and in vivo.
MCF-7 cells were treated with UCN-01, TAM, or UCN-01 combined with TAM at various concentrations in vitro. The antitumor effect was evaluated as the inhibition rate (I.R.%) by MTT assay. Two human breast carcinoma xenografts in nude mice, MCF-7 and Br-10, were treated with UCN-01, TAM or both agents together. The expression of p21 and the phosphorylation status of Rb protein in MCF-7 cells were detected by Western blotting.
UCN-01 or TAM alone inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. Combined treatment with UCN-01 followed by TAM inhibited the growth of MCF-7 cells synergistically and no significant differences in cytotoxicity were observed between the different sequences of UCN-01/TAM and TAM/UCN-01. Combination treatment with UCN-01 and TAM against MCF-7 and Br-10 in vivo exhibited superior antitumor effects compared with either agent treatment alone. Although 0.1 microg UCN-01 per ml (I.R.: 48.1%) or 2 microM TAM (I.R.: 31%) induced p21 expression, phosphorylation of Rb protein was not inhibited. However, combination treatment with UCN-01 and TAM at the same concentrations resulted in an I.R. of 67% and dephosphorylation of Rb protein.
The present study suggests that combining UCN-01 and TAM could result in augmented cytotoxicity because of their similar mechanism of action. This combination may have potential clinical applications for breast cancer treatment, by reducing the toxicity of UCN-01.
7-羟基星孢菌素（UCN-01）最初作为一种蛋白激酶C抑制剂被分离出来，并已显示出对多种人类癌细胞系具有抗肿瘤活性。UCN-01抑制细胞周期从G1期进入S期，与细胞周期蛋白依赖性激酶（CDK）活性的抑制及内源性CDK抑制剂p21的诱导有关，导致视网膜母细胞瘤（Rb）蛋白的去磷酸化。他莫昔芬（TAM）使癌细胞停滞于G1期，提示TAM的作用机制与UCN-01相似。本研究旨在评估UCN-01联合TAM对人乳腺癌细胞的体内外抗肿瘤活性。
体外以不同浓度的UCN-01、TAM或UCN-01联合TAM处理MCF-7细胞。通过MTT法将抗肿瘤作用评估为抑制率（I.R.%）。用UCN-01、TAM或两种药物联合处理裸鼠体内的两种人乳腺癌异种移植瘤，即MCF-7和Br-10。通过蛋白质印迹法检测MCF-7细胞中p21的表达及Rb蛋白的磷酸化状态。
单独使用UCN-01或TAM均以浓度依赖性方式抑制MCF-7细胞的增殖。UCN-01后接TAM的联合处理协同抑制MCF-7细胞的生长，且UCN-01/TAM和TAM/UCN-01的不同给药顺序之间未观察到细胞毒性的显著差异。与单独使用任一药物相比，UCN-01和TAM联合处理对体内的MCF-7和Br-10表现出更强的抗肿瘤作用。虽然每毫升0.1微克UCN-01（I.R.：48.1%）或2微摩尔TAM（I.R.：31%）诱导p21表达，但Rb蛋白的磷酸化未被抑制。然而，相同浓度的UCN-01和TAM联合处理导致抑制率为67%且Rb蛋白去磷酸化。
本研究表明，由于UCN-01和TAM作用机制相似，联合使用可能会增强细胞毒性。这种联合可能通过降低UCN-01的毒性而在乳腺癌治疗中具有潜在的临床应用价值。
